A centrifugal compressor used for a rotary machine such as an industrial compressor, a turbo refrigerator, and a small gas turbine includes an impeller provided with a plurality of blades on a disc fixed to a shaft. The centrifugal compressor gives pressure energy and speed energy to a gas by rotating the impeller.
FIG. 6 is an explanatory view of a rotary machine of the related art that includes an impeller 201.
For example, a rotary machine of PTL 1 includes the impeller 201 constituted by a disc 203, a blade 204, and a cover 206. At a predetermined position of the impeller 201 in an axial direction, a sleeve portion 205 is formed integrally with the impeller 201. By performing shrinkage-fitting of the sleeve portion 205 to the shaft 202 at the predetermined position, the impeller 201 is fixed to the shaft 202.
PTL 1 discloses that when an internal radius of the sleeve portion 205 is set to R and a thickness in the range of the length L is set to T, the length L in which the centrifugal force of the impeller 201 does not affect the sleeve portion 205 is expressed by the following expression (1).[Expression 1]L≧1.8√{square root over (RT)}  (1)
That is, PTL 1 discloses that the influence of the radial displacement of the inner diameter of the impeller 201 due to the centrifugal force during rotation to the sleeve portion 205 is suppressed by setting the length L so as to satisfy the expression (1), and the stable operation is maintained without deviation of the impeller 201 and the shaft 202.